This application is a 371 of PCT/EP95/02919, filed on Jul. 24, 1995.
The present invention concerns a method for the determination of a specific immunoglobulin using antigens that comprise several epitope regions.
The detection of immunoglobulins in body fluids, in particular in human sera, is used to diagnose infections with microorganisms, in particular viruses, such as HIV, hepatitis viruses etc. The presence of specific immunoglobulins in the examined sample is usually detected by reaction with one or several antigens that react with the specific immunoglobulins. Methods for the determination of specific immunoglobulins in the sample liquid must be sensitive, reliable, simple and rapid.
In recent years more and more detection systems based on non-radioactive marker groups have been developed in which the presence of an analyte, e.g. a specific antibody, in the examined sample can be determined with the aid of optical (e.g. luminescence or fluorescence), NMR-active or metal-precipitating detection systems.
EP-A-0 307 149 discloses an immunological test for an antibody in which two recombinant polypeptides are used as antigens one of which is immobilized on a solid phase and the other carries a marker group and both recombinant antigens are expressed in different organisms to increase the specificity of the test.
EP-A-0 366 673 discloses a method for the detection of antibodies in a sample in which an antibody is detected by reaction with a purified labelled antigen and with the same purified antigen in a solid phase-bound form. Human IgG is for example disclosed as an antigen.
EP-A-0 386 713 describes a method for the detection of antibodies against HIV using two solid supports in which various HIV antigens are immobilized on the two solid supports each of which is brought into contact with an aliquot of a sample and with a labelled HIV antigen wherein the presence of antibodies is detected by a positive reaction in at least one of the tests. Recombinantly produced polypeptides are disclosed as HIV antigens.
EP-A-0 507 586 describes a method for carrying out an immunological test for a specific immunoglobulin in which a sample is brought into contact with two antigens capable of binding the immunoglobulin, wherein the first antigen carries a group suitable for binding to a solid support and the second antigen carries a marker group. The marker group can be a direct marker group e.g. an enzyme, a chromogen, a metal particle, or also an indirect marker group i.e. the marker group attached to the antigen can react with a receptor for the marker group which in turn carries a signal-generating group. A fluorescein derivative is mentioned as an example of such an indirect marker group, the receptor of which is an antibody which in turn is coupled to an enzyme. Polypeptides such as the hepatitis B surface antigen are disclosed as antigens. SH groups are introduced into this antigen by derivatization which are used to couple the fluorescein.
EP-A-0 507 587 discloses a specific method for the detection of IgM antibodies in which the sample is incubated with a labelled antigen which is directed against the antibody to be detected and with a second antibody which is also directed against the antibody to be detected and is capable of binding to a solid phase.
However, the immunological methods of detection according to the bridge test concept which are known from the state of the art in which a labelled antigen and an antigen capable of binding to a solid phase are used, still have major weaknesses. In particular they have a low sensitivity when a relatively low affinity is present between the antibody to be determined and the antigen. This is especially the case for a seroconversion that has occurred only recently and/or when new subtypes of the infectious microorganism occur. A further disadvantage of the previously known bridge test concepts is the risk of a false negative evaluation of high-titre samples due to the Hook effect.
The object of the present invention was therefore to provide a method for the detection of specific antibodies in which the disadvantages of the state of the art are at least partially eliminated and which has an adequate sensitivity especially in the case of a seroconversion which has only recently occurred and in the case of new microorganism subtypes. In addition the method according to the invention is intended to reduce the Hook effect.